1. Field of Invention
The invention relates to a process for immobilizing mercury by producing crystalline mercury sulfide for subsequent disposal of the mercury sulfide, the mercury sulfide being formed by the reaction of elemental mercury and an additive material of elemental sulfur or a sulfur compound.
2. Description of Related Art
Due to its special physical properties, mercury is used in many technological applications and in industrial production. Here, especially electrolysis of alkali-metal chlorides is used to recover chlorine. In addition to a plurality of positive properties, mercury is, however, a toxic, hazardous material which constitutes a danger to man and the environment especially as a result of its vapor pressure which is comparatively high at room temperature. Numerous accidents and almost irreversible environmental damage in the past have helped mercury to a doubtful popularity.
Against this background, nowadays, in many areas, mercury or entire production processes are being replaced to reduce the use of mercury, and thus, mercury emissions, as much as possible. The reduced demands lead to a reduction through termination of production of primary mercury at known production facilities. For many years secondary mercury has been recovered from scrap in recycling installations and offered on the market as an alternative to primary mercury. Very large amounts of secondary mercury will be made available in the future with the worldwide conversion of existing chlorine production from amalgam processes to membrane processes. Over the long term, it will not be possible to use the mercury made available from these installations in other environmentally safe applications. Against this background, it becomes necessary to make available an environmentally safe, final disposal possibility for elemental mercury.
One possibility of conversion of elemental mercury into a stabilized mercury compound consists in producing mercury sulfide (cinnabar). Mercury sulfide is a stable or stabilized compound which, as a result of its properties (nontoxic, chemically stable, and even under corrosive conditions), allows permanent and safe storage of mercury. Otherwise, it is fundamentally also possible to produce mercury sulfide using sulfur compounds.
U.S. Pat. No. 5,034,054 discloses a process for producing a stabilized mercury compound for subsequent disposal. Here, mercury is bound in the form of an amalgam in conjunction with copper, zinc or nickel as the additive material or as mercury sulfide in conjunction with sulfur as the additive material, and then, is disposed of in an environmentally safe manner. In the known process, the additive material is added to the mercury in a stoichiometric ratio of at least 1:1 and preferably 3:1. The mixing process is carried out at room temperature and ambient pressure. The disadvantage of the known process is that the additive material must be added to the mercury in a highly superstoichiometric ratio in order to ensure a sufficient reaction of the mercury to the mercury compound. Another disadvantage of the known process is that, with respect to the highly superstoichiometric excess of the additive material which is added in powder form, is that, after treatment, portions of free sulfur are still present which can be a problem for further handling of the final product (fire prevention, aerosols).
U.S. Patent Application Publication 2008/0019900 A1 discloses a process for producing mercury sulfide by the reaction of liquid mercury with solid sulfur. The process is carried out in a rotating reactor which is formed of a piston, a pipe attached to it and a feed device for adding mercury and sulfur. The reaction takes place at 20° C. to 100° C., preferably at 60° C. to 80° C., at ambient pressure.